In a can-annular gas turbine combustor, differences in air and fuel flow between combustor baskets produce differences in the dynamic pressure and NOx emissions. Typically, dynamic pressure and NOx emissions vary inversely such that as a combustion system is tuned to reduce NOx emissions, dynamic pressure increases. In a traditional dry low NOx (DLN) combustion system, there are four stages: an upstream premixing stage, a non-premixed pilot stage and two main premixing stages. Because the pilot flame burns as a high temperature diffusion flame, the production of NOx and the amount of dynamic pressure in a combustor basket are closely related to the pilot fuel fraction. Ideally, all of the fuel would be premixed prior to being introduced into the combustor basket to reduce NOx production. However, maintaining stable combustion in a combustor basket is very difficult to achieve without having a relatively high temperature region, typically referred to as the pilot region, that produces a relatively high amount of NOx.
One conventional system, which is a SIEMENS fuel system known as ACDMS, controls fuel flow to the pilot diffusion stage with a set of rules designed to optimize NOx production and operate the engine within dynamic limits. The dynamic pressure is measured in all combustor baskets in specific frequency ranges and the peak pressure value out of all the combustor baskets is used to adjust the fuel flow to the pilot diffusion stage. Hence, the operation of the gas turbine is based on the worst basket from a dynamic pressure perspective and the best basket from a NOx production perspective. Because the individual combustor fuel supply lines are connected to a common fuel manifold, adjusting the system based upon the peak combustor basket with the highest dynamic levels brings the peak combustor back within dynamic limits, however, the system is not optimized as other combustors are operating below the dynamic limits leaving unused margin for NOx optimization in the other combustor baskets. As a result, such decrease in NOx is not as large as it could be. Thus, a need exists for a more efficient manner of controlling pilot nozzle fuel flow such that dynamic pressures are within an acceptable range and NOx production is limited as much as possible.